Winter huddling groups in the striped mouse

Huddling is a strategy to avoid heat loss and thus save energy and is often observed in birds and rodents, which, because of their small body size, are prone to relatively high heat loss. Huddling might thus explain group-living in some cases, such as the winter huddling groups described for several northern hemisphere rodents. Here we describe winter huddling groups in an African rodent, the striped mouse (Rhabdomys pumilio (Sparrman, 1784)), from the Succulent Karoo of South Africa. Striped mice were radio-tracked and observed directly in the field. The importance of huddling in this species was demonstrated by comparing data collected over 2 years. The 2003 winter was characterized by a severe drought and 99% mortality. As a result, close kin were mainly unavailable and striped mice slept in non-kin huddling groups. In 2004, normal winter rainfall occurred, mortality was only 50%, and striped mice formed family groups that shared a nest at night. While family groups were stable in 2004, non-kin huddling groups in 2003 were highly flexible and often changed from night to night. Huddling groups are important for striped mice to save energy, and the instability of non-kin sleeping groups indicates that the potential for conflict is higher between non-kin than between kin and that there is a trade-off between thermoregulatory requirements and kin selection.